Shadow business secretary Chuka Umunna said Labour decided "swiftly and strongly" to refer the Falkirk selection controversy to the police.
He told BBC Radio 4's World at One: "I can confirm that we took advice yesterday in relation to the Falkirk matter and as a result of the advice given, have decided swiftly and strongly to refer it to the police.
"There is absolutely no place in the Labour Party for machine politics of this type, and where we find it we will root it out and stamp on it. It is not a way to conduct things within a constituency party."
Pressed on whether Labour would be publishing the internal report, Mr Umunna stressed that evidence had been gathered on a "confidential" basis.
"We are not publishing it," he added.
Conservative MP Henry Smith has written to Scottish police asking them to investigate whether trade union Unite "are guilty of committing fraud in Falkirk".
Labour is to refer its report on alleged irregularities in the selection of an election candidate in Falkirk to the police, a senior party source told the Press Association.
Labour leader Ed Miliband said Unite general secretary Len McCluskey's claims that the trade union was the victim of a "smear campaign" were "total nonsense".
He added that Mr McCluskey should not be "defending this kind of machine politics" when referring to the Falkirk selection controversy.
Labour leader Ed Miliband said he would not allow the party's name to be "undermined by the behaviour of a few individuals" as the row over the Falkirk selection controversy continues to escalate.
Speaking at a charity event in London today, Mr Miliband said: "The Labour Party I lead will select its candidates in a fair and transparent way. We will act without fear or favour.
"Instead of defending what happened in Falkirk, Len McCluskey should be facing up to his responsibilities. He should not be defending the machine politics involving bad practice and malpractice that went on there, he should be facing up to it."
Mr Miliband said: "It's wrong because we had members being signed up without their knowledge, bad practice, malpractice and frankly instead of defending that kind of thing Len McCluskey should be condemning it."
He added: "Let nobody be in any doubt, there is only going to be one outcome to this: the Labour Party will act in a way that upholds the integrity of our party, the integrity of our party members and the integrity of ordinary trade union members.
"I will not allow the good name of the Labour Party to be undermined by the behaviour of a few individuals."
Ed Miliband is waiting for a "phone call from Unite or divine inspiration through the ether" before deciding whether he backs a referendum on Britain's membership of the European Union, William Hague said.
The Foreign Secretary taunted the Labour leader for not attending the Commons debate in a week when his general election co-ordinator Tom Watson resigned over the party's controversial links with the Unite union.
In a resignation letter Mr Watson praised Mr Miliband for his "Buddha-like qualities".
Mr Hague said: "The leader of the opposition isn't even here, presumably he is sitting somewhere wondering whether his instructions will come in a phone call from Unite or divine inspiration through the ether, because there is no other way in which he is able to decide on this Bill."
Tom Watson said he had been thinking about quitting as Labour election co-ordinator "for a few months", because he found the post very tiring and felt unable to speak out on issues of concern.
He told BBC Radio WM: "We have had all this fuss over Falkirk and I just thought to myself, if I am getting into the story and not being useful any more for Ed, then it's time to move.
Asked about the details of what had happened in Falkirk, he said: "I really don't know about that. One of the things I did on Falkirk was keep out of that process, because there's an employee of mine who was a candidate.
"I know this works - people put two and two together and very often get five, but that's not the reason I have gone. The Falkirk thing crystallised in my mind how difficult it would be for me to stay in the post."
He added: "I've had an unusual journey in politics. There are some people who have never quite forgiven me for resigning in 2006 under Tony Blair and I accept that completely. What I don't want to be is a problem for Ed Miliband, so going to the backbenches is the best thing.
"I want him as Prime Minister and he has got my full support."
Tom Watson, who resigned from the shadow cabinet yesterday over the Falkirk selection controversy, said the Conservative party's portrayal of trade union Unite being in control of Labour was "just not true".
Speaking to BBC Radio WM, Mr Watson said: "Looking at how the unions organise within the Labour Party, I genuinely think they are pretty hopeless. I don't think there's many trade union activists who get much of a say these days. I don't think it's a problem.
"I do think there's a lot of politics behind it. Obviously David Cameron would like people to believe that the Labour Party is in the hands of these left-wing factions. It's just not true.
"We've got to sort these arrangements out - clearly something had gone wrong in Falkirk that needs sorting out - but I think David Cameron's portrayal of the situation, that everyone is in hock to Len McCluskey, is just not true."
David Cameron criticised Ed Miliband's leadership of Labour, saying he needed to get a "grip" of his party after the Falkirk selection controversy.
The Prime Minister said: "It's quite clear the trade unions have far too much control over Labour.
"This has happened on Ed Miliband's watch. It is something of a scandal that is unfolding and he badly needs to grip it".
Labour's shadow leader of the Commons Angela Eagle said Unite general secretary Len McCluskey was entitled to express his own opinion on calling for the internal inquiry on Falkirk to be released but it was Ed Miliband who would decide what should be done.
Ms Eagle told BBC Radio 4's Today programme: "Len McCluskey can have an opinion on that, but it is the internal party Labour structures which will decide on how we protect the integrity of our rules.
She added: "We will not tolerate the kind of behaviour we have seen in Falkirk, whoever is responsible for it. There is sufficient evidence of misbehaviour amongst particular individuals up in Falkirk to justify the action that the leader of the Labour Party took yesterday."
Responding to Ms Eagle's comments, Labour's former general secretary Peter Watt - who held the post from 2005 to 2007 - said on Twitter:
If Labour attempts to blame #Falkirk just on 'particular individuals' rather than accepting institutional problem it will be a disgrace.